The present invention relates to wireless power supplies and more particularly to inductive power supplies.
With the widespread and continually growing use of portable electronics, there is an ever-increasing need for wireless power supply system that are capable of charging and/or powering electronic devices without the need for direct wired connections. Wired connections suffer from a variety of problems that make them inconvenient, burdensome and aesthetically unpleasing. Perhaps most notably, wired connections require physically plugging and unplugging the device, involve a mess of unsightly cords, require matching plugs on the cord and remote device and can only charge a single device at a time with a single cord. Further, with conventional paired chargers, a user is required to keep and store as many wired DC power supplies as devices that are owned.
Wireless power supply systems have proven to be a dramatic improvement over wired connections. Wireless power supply systems eliminate the need to connect electronic devices to power cords and therefore eliminate many of the problems associated with wired connections. Many conventional wireless power supply systems rely on inductive power transfer (i.e. the transfer of power using electromagnetic fields) to convey electrical power without wires. A typical inductive power transfer system includes an inductive power supply that uses a primary coil to wirelessly convey energy in the form of a varying electromagnetic field and a remote device that uses a secondary coil to convert the energy in the electromagnetic field into electrical power. To provide an inductive power transfer system with optimal efficiency, it is typically desirable to provide proper alignment between the primary coil and the secondary coil. Alignment is often achieved using cradles or other similar structures. For example, the primary coil may be positioned around the outside of a cup shaped receptacle to closely receive the portion of the remote device containing the secondary coil. When the remote device is placed in the cup, the two coils become closely aligned by the mechanical interfit. Although helpful in providing alignment, this approach requires deliberate placement of the remote device within the cradle and essentially precludes movement of the electronic device with respect to the power supply. It may also limit the inductive power supply to use in connection with a single device specially configured to fit within the cup or cradle. It also limits the ease of interchangeability with multiple devices containing secondary coils. The cup-shaped receptacle in the charger will, by definition, provide a close interfit with the secondary device it was designed for. However, for other devices, it may provide a loose fit or a receptacle too small to allow any fit at all.
In another conventional application, an electronic device is provided with a matching wireless charger. In this construction, the wireless charger includes a fixed peg that extends upwardly to provide a mounting structure to receive the electronic device for charging. The device defines a void configured to fit closely over the peg. In use, the device is docked on the wireless charger by placing it on the wireless charger with the void fitted over the peg. In this construction, the primary coil and the secondary coil are positioned to provide appropriate alignment when the remote device is properly docked on the wireless charger. Although this construction provides good alignment between the electronic device and its matching wireless charger, it may suffer from a variety of issues. For example, the peg is fixed and therefore does not provide any freedom of movement for the remote device. Further, the fixed peg extends from the charging surface at all times (even when a remote device is not present), thereby interfering with use of the charging surface for other purposes.
In yet another conventional application, magnets are used to draw the primary coil and secondary coil into close alignment. For example, in one conventional application, the primary coil is coupled with a primary magnet and loosely fitted within a void beneath the charging surface. When a remote device with a secondary magnet is placed on the charging surface within sufficient proximity to the primary magnet, the magnetic attraction of the primary magnet and the secondary magnet moves the primary magnet through the void into alignment with the secondary magnet. This, in turn, draws the primary coil and the secondary coil into close alignment. Although providing some improvement, the force of the magnetic attraction may not be sufficient to move the primary magnet and primary coil within the void. This is particular true when the remote device is initially placed on the charging surface in a position in which the primary magnet and the secondary magnet are not already in close alignment. Further, because the primary magnet and primary coil are permitted to move freely within the void, their location may be unknown when initially placing the remote device on the charging surface. This may make it more difficult to initially bring the two magnets together.